1. Field of the Invention
The present invention relates to an exhaust pipe support, and in particular to an improved structure of an exhaust pipe support that is suitably used for supporting an exhaust pipe of a vehicle such as automobile to the vehicle body in a vibration damping fashion.
2. Discussion of Related Art
Generally, an exhaust pipe of engine (internal combustion engine) in a vehicle such as automobile is connected to the engine at a front end thereof which is positioned at a front side in the frontward and backward direction of the vehicle. At the middle and rearward thereof, the exhaust pipe is elastically suspended and supported to the vehicle body via an exhaust pipe support made of a predetermined elastic supporting member, which is a so-called muffler support.
As one type of exhaust pipe support, there is known an exhaust pipe support comprising an elastic body having a ring shape for suspending an exhaust pipe from a vehicle body. Such an elastic body has, in its upper part, an upper attachment portion which is provided with an upper attachment hole extending parallel with an axial direction of the elastic body and into which a supporting member of a vehicle body side is to be inserted, and in a lower part of the elastic body located symmetrically to the upper part where the upper attachment portion is disposed, a lower attachment portion which is provided with a lower attachment hole extending parallel with the axial direction of the elastic body and into which a supporting member of an exhaust pipe side is to be inserted, and further a pair of arm portions which extends in the vertical direction to mutually connect the upper attachment portion and the lower attachment portion. In the exhaust pipe support having such a structure, vibration is transmitted from the exhaust pipe to the vehicle body or from the vehicle body to the exhaust pipe by driving of engine, traveling of vehicle and the like, and the transmitted vibration is absorbed or reduced by elastic deformation of the pair of arm portions.
However, in such a conventional exhaust pipe support, when large tensile stress and compression stress is applied to the pair of arm portions in the vertical direction due to input vibration, a phenomenon of surging occurs by which the pair of arm portions vibrates in both directions perpendicular to the vertical and axial directions of the ring-shaped elastic body composing the exhaust pipe support, especially in antiphase. When such a surging phenomenon occurs, an absolute spring constant of the supporting apparatus as a whole (mainly of the pair of the arm portions of elastic body) becomes extremely large in a high frequency range of 500 Hz or higher and vibration transmissivity increases. This may cause the problem of deterioration in damping effect.
In such a circumstance, there is proposed an exhaust pipe support having a so-called O-shape which has a center connecting part formed of elastic material in the inside space of the ring-shaped elastic body to mutually connect middle parts of the pair of arm portions (see, U.S. Pat. No. 5,050,837, for example). In the exhaust pipe support having such a structure, the vibration caused by the surging phenomenon in the high frequency range as described above can be moderated by tension and compression effects of the center connecting part. As a result, the absolute spring constant in the high frequency range of the whole of the supporting apparatus is advantageously reduced, thereby advantageously improving vibration damping effect.
However, inventors of the present application examined vibration damping performance of such a conventional θ-shaped exhaust pipe support in various ways, and found that such a θ-shaped exhaust pipe support has a problem related to vibration damping that is not observed in the conventional so-called O-shaped exhaust pipe support not having a center connecting part.
Specifically, a natural frequency of the center connecting part made of elastic material, which is provided in the conventional θ-shaped exhaust pipe support is generally about 300 Hz. Therefore, it was found that in the θ-shaped exhaust pipe support having such a center connecting part, surging phenomenon occurs in the middle to low frequency range of about 300 Hz, and the absolute spring constant of the whole of the supporting apparatus is increased to some extent, though not to the extent of increase in the high frequency range of the O-shaped exhaust pipe support. As a result, the vibration damping effect inevitably decreases in the middle to low frequency range of about 300 Hz.